The present invention relates to a fluid dispensing apparatus, primarily though not exclusively for use in ink jet printers.
The use of piezoelectric transducers in fluid dispensing apparatus such as ink jet printers is becoming increasingly widespread. A recorder operating with drops of liquid is disclosed in U.S. Pat. No. 4,072,959 in which rod-shaped piezoelectric transducers are located in front of inlet openings to nozzles. The piezoelectric transducers are secured at one end in a housing which contains the ink to be expelled, while the free ends of the transducers cover the inlet openings. When applying an electrical potential across a transducer, the transducer bends away from the inlet opening. If the applied potential is briefly interrupted, the transducer snaps back to the unbent position and thereby squeezes a drop of ink through the nozzle. It is to be noted that the recorder disclosed in this document cannot be used for dispensing fluid under pressure since the piezoelectric transducers cannot seal the inlet openings to the nozzles.
A fluid control device for controlling the flow of fluid under pressure is disclosed in U.S. Pat. No. 4,629,926. In said device, a piezoelectric spring-like bender is operatively associated with an impacting member. The impacting member is capable of deforming a membrane to control flow past a valve seat upon change in the electrical condition of the bender. Each bender and impacting member is isolated from the fluid by the membrane, with the membrane thus acting as a seal against the valve seat. In order to ensure adequate sealing, the bender must be capable of counteracting the pressure in the fluid acting on the membrane when the fluid control device is in its closed position.
A flow control valve 44 ng a piezoelectric spring-like bender which acts directly on a valve seat is described in U.S. Pat. No. 4,340,083. The valve in said document is designed to provide a substantially constant flow independent of changes in the pressure differential thereacross and/or to exert a minimum closing force against the seat so as to provide a substantially fluid-tight seal therewith in the absence of a command signal applied to the bender. In order to open the flow control valve, the bender must overcome the force acting on the bender as a result of the fluid pressure.
Particularly in ink jet printer heads, a need exists for high frequency, high resolution, long printing distance, robust, reliable and inexpensive devices. There is also a wish to have greater freedom when formulating inks. It is therefore an object of the present invention to provide such a device.
The above object is achieved by fluid dispensing apparatus for selectively dispensing desired quantities of a fluid under pressure, the apparatus comprising a base plate having a dispensing passage extending about a first axis; a valve arrangement associated with the dispensing passage, and a piezoelectric transducer acting on the valve arrangement to effect displacement of the valve arrangement between a first position in which the dispensing passage is closed and a second position in which the dispensing passage is connected to a source of said fluid under pressure. In accordance with the present invention, the valve arrangement comprises a slide valve, with the slide valve and piezoelectric transducer being arranged such that during at least initial displacement of the valve arrangement from the second position towards the first position, the slide valve is displaced in a direction transverse to the first axis.
By using a slide valve, the dispensing passage can be opened and closed without resorting to a lifting arrangement. This implies that the two functions previously effected by the transducer, namely sealing and displacing the valve arrangement, are separated, thereby simplifying the arrangement and allowing i.a. lower energy consumption.
In one embodiment of the invention, the slide valve comprises a valve plate arranged for translational displacement, either by an axial displacement of the piezoelectric transducer or by a transverse displacement thereof.
In a further embodiment, the slide valve comprises a valve plate arranged for rotational displacement, again either by an axial displacement of the piezoelectric transducer or by a transverse displacement thereof.